Note: There are issues with Exchange 2013 CU14 and Exchange 2016 CU3 with regards to failing Content Indexing. Fellow MVP Jaap Wesselius blogged about this here. For now, recommendation is to not upgrade to CU14, until further notice. Also, there are acknowledged issues when running Exchange 2016 CU3 on Windows Server 2016. Don’t deploy Exchange 2016 CU3 on that OS until further notice.

Today, the Exchange Team released the september updates for Exchange Server 2013 and Exchange Server 2016.

The biggest changes are for Exchange Server 2016:

• Exchange Server 2016 CU3 or later support on Windows Server 2016, which is expected to be released at Ignite next week. Windows Server 2016 Domain Controllers are supported; requirement is just Forest Functional Level at Windows Server 2008 R2 or later. Note that it is also announced Exchange Server 2013 will not be supported (as in: now, and in the future). Performance-wise, it is recommended to exclude Exchange setup and log folders, as well as the noderunner processes in Windows Defender.
• Finally, Exchange Server 2016 CU3 introduces the long-awaited Read from Passive feature. This means, indexes will be generated using (local) passive databases copies, and no longer require coordination with the server holding the active database copy. The result is lower bandwidth requirements, and – compared to Exchange Server 2013 – faster fail-overs. Be advised this feature does not apply to lagged copies.
• An update for the Mailbox Server Role Calculator(s) for Exchange 2016 is available now (v8.3), incorporating Read from Passive changes. This allows organizations to not only size their deployment, but also predict the positive effect on bandwidth usage for current environments as well by using numbers. You can download the calculator here.

For a list of fixes in these updates, see below.

Exchange 2016 CU3 fixes:

Exchange 2013 CU14 fixes:

These Cumulative Updates for Exchange Server 2016 and 2013 include the security update released last week, MS16-108. The Cumulative Updates for Exchange Server 2016 and 2013 also include DST changes.

Notes:

• Exchange 2016 CU3 includes schema changes (version 15326, reference), and Exchange 2016 CU3 as well as Exchange 2013 CU14 may introduce RBAC changes in your environment. Where applicable, make sure you run /PrepareSchema to update the schema or /PrepareAD to apply RBAC changes, before deploying or updating Exchange servers. To verify this step has been performed, consult the Exchange schema overview.
• When upgrading your Exchange 2013 or 2016 installation, don’t forget to put the server in maintenance mode when required. Do note that upgrading, before installing the Exchange binaries, setup will put the server in server-wide offline-mode.
• Using Windows Management Framework (WMF)/PowerShell version 5 on anything earlier than Windows Server 2016 is not supported. Don’t install WMF5 on your Exchange servers running on Windows Server 2012 R2 or earlier.
• When using Exchange hybrid deployments or Exchange Online Archiving (EOA), you are required to stay current.
• If you want to speed up the update process for systems without internet access, you can follow the procedure described here to disable publisher’s certificate revocation checking.
• Cumulative Updates can be installed directly, i.e. no need to install RTM prior to installing Cumulative Updates.
• Once installed, you can’t uninstall a Cumulative Update nor any of the installed Exchange server roles.
• The order of upgrading servers with Cumulative Updates is irrelevant.

Caution: As for any update, I recommend to thoroughly test updates in a test environment prior to implementing them in production. When you lack such facilities, hold out a few days and monitor the comments on the original publication or TechNet forum for any issues.